German Chancellor Angela Merkel (R) and Foreign Minister Guido Westerwelle attend a debate on the euro rescue package in the Bundestag, the lower house of parliament, in Berlin May 21, 2010. REUTERS/Thomas Peter

Support for the pro-business FDP, junior coalition partners to Merkel’s conservatives, has plunged following the party’s failure to push through key campaign objectives and a string of negative headlines for Westerwelle, Germany’s foreign minister.

Ructions within the FDP, whose flagship plans to cut taxes have foundered, could undermine government efforts both to agree measures aimed at shoring up confidence in German public finances, and present a united front in support of the euro.

Infighting in the FDP hit the headlines last week after Wolfgang Gerhardt, a former FDP leader, attacked Westerwelle for failing to give the party a clear profile on foreign policy just as the Free Democrats’ standing slumped to a new low in polls.

The row intensified on Saturday as FDP Justice Minister Sabine Leutheusser-Schnarrenberger said the party’s leadership had lost its way in an interview with German weekly Der Spiegel.

“All in all, the image of the FDP is not how one would wish it to be,” Leutheusser-Schnarrenberger told the magazine. “And that image obviously feeds off the people at the head of it.”

Asked whether Westerwelle, who is also Germany’s vice chancellor, was still the right person to chair the party he has led since 2001, Leutheusser-Schnarrenberger said, “He is the elected party leader.”

The 58-year-old Leutheusser-Schnarrenberger is a respected figure in the party and the only FDP member of the cabinet to have previously held government office, serving as justice minister between 1992 and 1996 under ex-chancellor Helmut Kohl.

Her criticism of Westerwelle compounds a difficult month for the FDP, which could soon be ousted from the regional government of Germany’s most populous state, North Rhine-Westphalia (NRW), after a disappointing showing in a May 9 vote.

After taking some 14.6 percent of the national vote in last September’s federal election, the FDP could not muster even half that amount in NRW, polling just 6.7 percent. Merkel’s Christian Democrats also suffered heavy losses in the vote.

Latest opinion polls show the rot has not stopped there.

Only six percent of voters said they would back the FDP in a federal election in the latest monthly gauge of sentiment by ZDF television. A more short-term measure of the mood in the ZDF study put public support for the FDP at just three percent.

Roland Sturm, a political scientist at Erlangen-Nuremberg University, told Reuters this week Westerwelle’s position did not look under threat for now, but that pressure on him would mount if the FDP failed again in state elections next year.